Case report: Mafb promoter activity may define the alveolar macrophage dichotomy

Front Immunol. 2022 Dec 12:13:1050494. doi: 10.3389/fimmu.2022.1050494. eCollection 2022.


Cre-LoxP system has been widely used to induce recombination of floxed genes of interest. Currently available macrophage promoter-specific Cre recombinase mice strains have various limitations that warrants the testing of additional Cre strains. V-maf musculoaponeurotic fibrosarcoma oncogene family, protein b -Cre (Mafb-Cre) mice label macrophages in most organs such as spleen, small intestine, lung, bone marrow, and peritoneal cavity. However, whether Mafb-Cre recombinase targets the gene recombination in alveolar macrophage remains untested. Here, we utilized MafbCre/WTR26mTmG/WT strain that expresses mTOM protein in all the cells of mouse body except for those that express Mafb-Cre-regulated mEGFP. We performed fluorescent microscopy and flow cytometry to analyze mTOM and mEGFP expression in alveolar macrophages from MafbCre/WTR26mTmG/WT mice. Our analyses revealed that the Mafb-Cre is active in only ~40% of the alveolar macrophages in an age-independent manner. While Mafb- (mTOM+/mEGFP-) and Mafb+ (mEGFP+) alveolar macrophages exhibit comparable expression of CD11b and CD11c surface markers, the surface expression of MHCII is elevated in the Mafb+ (mEGFP+) macrophages. The bone marrow-derived macrophages from MafbCre/WTR26mTmG/WT mice are highly amenable to Cre-LoxP recombination in vitro. The bone marrow depletion and reconstitution experiment revealed that ~98% of alveolar macrophages from MafbCre/WTR26mTmG/WT → WT chimera are amenable to the Mafb-Cre-mediated recombination. Finally, the Th2 stimulation and ozone exposure to the MafbCre/WTR26mTmG/WT mice promote the Mafb-Cre-mediated recombination in alveolar macrophages. In conclusion, while the Mafb-/Mafb+ dichotomy thwarts the use of Mafb-Cre for the induction of floxed alleles in the entire alveolar macrophage population, this strain provides a unique tool to induce gene deletion in alveolar macrophages that encounter Th2 microenvironment in the lung airspaces.

Keywords: Cre-LoxP; MAFB; alveolar macrophages; lung; macrophage-specific Cre.

Publication types

  • Case Reports
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Lung / metabolism
  • Macrophages* / metabolism
  • Macrophages, Alveolar* / metabolism
  • MafB Transcription Factor / genetics
  • MafB Transcription Factor / metabolism
  • Mice
  • Promoter Regions, Genetic
  • Proteins / metabolism


  • Proteins
  • Mafb protein, mouse
  • MafB Transcription Factor